FUTUREWATCH: Self Assembling PV Cells

Newly published research from Rice University and Penn State show that some polymer-based organic PV devices can self-assemble. The research could make producing organic PV far easier and cost effective in the future.

The research, led by Rice’s Rafael Verduzco and Penn State’s Enrique Gomez—both chemical engineers, was recently published in the American Chemical Society’s journal Nano Letters. In creating the self-assembling devices, Rice’s lab discovered a block copolymer—P3HT-b-PFTBT—that separates into bands about 16 nanometers wide, according to Rice. “More interesting to the researchers was the polymers’ natural tendency to form bands perpendicular to the glass. The copolymer was created in the presence of a glass/indium tin oxide (ITO) top layer at a modest 165 degrees Celsius,” Rice said.

That was coupled with a layer of aluminum constructed by Penn State. “On the other side of the device constructed by the Penn State team, the polymer bands stretched from the top to bottom electrodes and provided a clear path for electrons to flow,” Rice said.

“On paper, block copolymers are excellent candidates for organic solar cells, but no one has been able to get very good photovoltaic performance using block copolymers,” Verduzco said. “We didn’t give up on the idea of block copolymers because there’s really only been a handful of these types of solar cells previously tested. We thought getting good performance using block copolymers was possible if we designed the right materials and fabricated the solar cells under the right conditions.”

Why the device assembles itself in the way it does isn’t completely understood yet. “Our hypothesis is that both polymers want to be in contact with the ITO-coated glass. We think that forces this orientation, though we haven’t proven it yet,” Verduzco said.

At this point the efficiency of the device is low at nearly 3 percent conversion efficiency. But even the organic PV devices have efficiency levels around 10 percent. While that lags far below the 24 percent efficiency of high-end silicon cells like SunPower’s Maxeon cells, organic PV is much cheaper to produce and can be used in more applications than silicon PV. For instance, some organic PV cells and modules are made, literally, by printing them out.

Now the team will experiment with other block copolymers in a bit to increase the efficiency of the devices. “We’ll focus on performance first, because if we can’t get it high enough, there’s no reason to address some of the other challenges like stability,” Verduzco said.

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